The present invention relates to a circuit for shaping a measurement-signal voltage into a square-wave signal.
A circuit of this kind is described in the journal "Elektronik", No. 10, May 17, 1985, p. 100. There an operational amplifier connected as a Schmitt trigger is used for shaping a measurement signal into a square-wave signal. The amplified measurement signal is applied to the positive input of the operational amplifier, and the supply voltage to the other, negative input. The supply voltage is assumed to be constant, so that a stabilized supply voltage must be present. Errors in the measurement signal are corrected by means of a voltage divider which includes a positive temperature coefficient resistor; that is, a resistor whose resistance increases with an increase in its temperature, and has its tap connected to one of the inputs of an operational amplifier. This gives a temperature-controlled current source for a sensor whose measurement-signal voltage is to be shaped. For temperature compensation, resistors which are not otherwise necessary are connected into the leads to the inputs of an operational amplifier.